A TORQUE DISTRIBUTION SYSTEM FOR A VEHICLE

Abstract

A torque distribution system for a vehicle permits the transfer of torque between vehicle wheels using a selectively engagable clutch that is hydraulically engaged using hydraulic pressure provided by a hydraulic transmission pump driven by the engine, allowing for enhanced system functionality and reduced part content in comparison with known torque distribution systems. The system may include an "active- on-demand" clutch that is selectively engagable to transfer torque between a front differential and a rear differential (thereby transferring torque from the front wheels to the rear wheels) as well as an electronically-limited slip differential clutch selectively engagable to transfer torque from one front wheel to the other front wheel through the front differential. Utilization of the transmission hydraulic pump allows pressure to be provided to engage the clutch even when the wheels are stationary, i.e., to launch the vehicle.

Full Text

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TORQUE DISTRIBUTION SYSTEM WITH ELECTRONICALLY-CONTROLLED
POWER TAKE-OFF MODULE
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of United States Provisional
Application No. 60/822,989, filed August 21, 2006, which is hereby incorporated by
reference in its entirety.
TECHNICAL FIELD
[0002] The invention relates to a system for distributing driving torque between
vehicle wheels and includes an electronic power take-off unit for same.
BACKGROUND OF THE INVENTION
[0003] The ability to control torque distribution among the wheels of a vehicle
improves vehicle traction. Torque distribution systems, also referred to as torque biasing
systems, include limited slip differentials having a clutch that is engagable to transfer
torque between left and rights wheels and active-on-demand systems, also utilizing a
selectively engagable clutch, to transfer torque between front and rear wheels. Existing
torque distribution systems typically require the addition of an electric motor-driven
pump for actuation of the clutch, thus increasing required componentry. Alternative
existing systems may engage the clutches using a pump that is actuated by a speed
difference between wheels, thus requiring that the vehicle be in motion for the system to
operate.
SUMMARY OF THE INVENTION
[0004] A torque distribution system for a vehicle permits the transfer of torque
between vehicle wheels using a selectively engagable clutch that is hydraulically engaged
using hydraulic pressure provided by an engine-driven pump, allowing for enhanced
system functionality and reduced part content in comparison with known torque
distribution systems. The system includes at least one torque-transmitting mechanism,

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such as an "active-on-demand" clutch that is selectively engagable to transfer torque
between a front differential and a rear differential (thereby transferring torque from the
front wheels to the rear wheels) and/or an electronically-limited slip differential clutch
selectively engagable to transfer torque from one front wheel to the other front wheel
through the front differential. Utilization of the transmission hydraulic pump, typically
present in a transmission for providing lubrication and cooling to transmission gears and
gear selection clutches, allows pressure to be provided to engage the clutch even when
the wheels are stationary, i.e., to launch the vehicle. This is not possible with limited slip
differential clutches that are actuated by hydraulic pressure provided by a pump that is
driven by a speed difference between two of the wheels to generate hydraulic pressure to
actuate the clutch. Braking of the vehicle is also not required in order to engage either
the electronically-limited slip differential clutch or the active-on-demand clutch.
Additionally, cost, weight, and packaging space savings and reduced electrical power
consumption may be realized with respect to systems requiring a separate motor and
pump to provide hydraulic pressure for clutch engagement.
[0005] Preferably, the clutch or clutches of the torque distribution system are
packaged as a module, referred to herein as an electronically-controlled power take-off
module, having its own casing mountable adjacent the transmission casing with a fluid
connection there between to allow the transmission pump to connect with the clutches.
An electronic controller may be used to control engagement of the clutches based on
vehicle operating information such as wheel speed, yaw rate, steering angle, and lateral
acceleration. The controller may also modulate the amount of hydraulic pressure
provided to the clutches to allow slipping engagement, with associated reduced torque
transfer, when desired.
[0006] Specifically, a torque distribution system for a vehicle having wheels and
a hydraulic pump includes at least one torque-transmitting mechanism selectively
engagable to transfer torque between at least two of the wheels. The hydraulic pump is
hydraulically connectable with the torque-transmitting mechanism(s) for controlling
engagement thereof. The hydraulic pump is driven by the engine and so can provide

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hydraulic pressure regardless of wheel speed. Preferably, the hydraulic pump also
provides lubrication and hydraulic pressure to the transmission.
[0007] The torque distribution system may utilize a first or front differential
mechanism having a first member operatively connected for driving rotation by an output
member of the transmission, a second member operatively connected for driving rotation
of the left front wheel and a third member operatively connected for driving rotation of
the right front wheel. The torque-transmitting mechanism may be a first friction clutch
that is selectively engagable to transfer torque between the second and third members,
thereby transferring torque between the left and right front wheels.
[0008] Additionally, a longitudinally-extending member such as a propeller shaft
spans at least partially between the front wheels and rear wheels. A rear differential
mechanism operatively connects the rear wheels with the longitudinally-extending
member. The torque-transmitting mechanism may be a clutch that is selectively
engagable for transferring torque between the front differential and the longitudinally-
extending member to thereby transfer torque between the front and rear wheels.
[0009] The torque distribution system may include an electronic controller that
receives a sensor signal correlated with at least one vehicle condition and then sends a
control signal based on the sensor signal and determinative of hydraulic pressure applied
to the torque-transmitting mechanism(s), thereby permitting controlled slip to vary the
amount of torque transferred by the torque-transmitting mechanism(s).
[0010] The torque distribution system may include a hydraulic control module
which operatively connects the electronic controller with the torque-transmitting
mechanism of the torque distribution system. The hydraulic control module includes a
first solenoid selectively actuatable by a control signal from the controller to allow
hydraulic pressure provided by the pump into fluid communication with the torque-
transmitting mechanism. Preferably, an accumulator and an additional solenoid are
provided. The additional solenoid is in fluid communication between the accumulator
and the first solenoid and is selectively actuatable and configured to permit hydraulic
flow to the first solenoid when actuated and prevent hydraulic flow to the first solenoid,
maintaining hydraulic pressure in the accumulator, when not actuated. A check valve or

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a second additional solenoid may be positioned between the hydraulic pump and the
accumulator to control fluid flow between the hydraulic pump and the accumulator.
Preferably, pressure sensors are operatively connected to each of the torque-transmitting
mechanisms to monitor apply pressure of the torque-transmitting mechanisms and
communicate the monitored pressure to the controller, thereby allowing feedback control
of clutch apply torque.
[0011] The torque-transmitting mechanisms, e.g., the active-on-demand clutch,
the electronically-limited slip differential clutch, and the electronic controller of the
torque distribution system, may be referred to as an electronically-controlled power take-
off module. The torque-transmitting mechanisms may be packaged in a module casing
that encloses the torque-transmitting mechanisms and is connectable to a transmission
casing for the transmission to permit fluid transfer from the transmission pump to the
torque-transmitting mechanisms through the connected transmission casing and module
casing. The different combinations of electronically-controlled solenoid(s), accumulator,
ball check valve, and pressure sensor(es) discussed herein, may be referred to as a
hydraulic control module that is part of the electronically-controlled power take-off
module
[0012] The above features and advantages and other features and advantages of
the present invention are readily apparent from the following detailed description of the
best modes for carrying out the invention when taken in connection with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIGURE 1 is a schematic illustration of a vehicle having a torque
distribution system with an electronic power take-off module including torque-
transmitting mechanisms;
[0014] FIGURE 2 is a schematic representation of the of the torque distribution
system of Figure 1 showing a hydraulic pump within the transmission and the
torque-transmitting mechanisms within the electronic power take-off module;

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[0015] FIGURE 3 is a schematic representation of a hydraulic control module for
the torque-transmitting mechanisms of Figure 2;
[0016] FIGURE 4 is a schematic representation of an alternative hydraulic control
module for the torque-transmitting mechanisms of Figure 2; and
[0017] FIGURE 5 is a schematic representation of another alternative hydraulic
control module for the torque-transmitting mechanisms of Figure 2.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] Referring to the drawings, wherein like reference numbers refer to like
components, Figure 1 shows a vehicle 10 powered by an engine 11. The engine 11 is
operatively connected to a transmission 12, contained within a transmission casing 14.
via a torque converter (shown in Figure 2). An electronically-controlled power take-off
module 16 has a module casing 18 connected to the transmission casing 14. Operation
and control of the electronic power take-off module 16 is described with respect to Figure
2. The power take-off module 16 is part of a torque distribution system 17 for
transferring torque between the left and right front wheels, 20, 22 via a front differential
mechanism (labeled 46 in Figure 2) contained within the transmission casing 14, and
between the front wheels 20, 22 and a rear differential mechanism 24 connected with rear
wheels 26, 28 via a propeller shaft 30, also referred to herein as a longitudinally-
extending member, used to connect the power take-off module 16 to the rear differential
mechanism 24.
[0019] Referring to Figure 2, the engine 11 has an output shaft 32 connected to a
transmission input member 34 via a torque converter 36. The engine 11 drives a pump
portion P of the torque converter 36 to which a hydraulic pump 38 is connected. The
hydraulic pump 38 provides hydraulic fluid for cooling a transmission gearing
arrangement 13, including hydraulically-actuated gear selection friction clutches (not
shown), located within the transmission casing 14 that are engagable to provide desired
speed ratios between the transmission input member 34 and a transmission output
member 40, as is understood by those skilled in the art. The output member 40 drives an
output gear 42 meshingly engaged with a carrier member 44 of the front differential

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mechanism 46 (relative size of gear 42, carrier member 44, engine 11 and transmission
12 not to scale). The front differential mechanism 46 also includes a left side gear 48 and
a right side gear 50 connected for respective rotation with the left and right wheels 20. 22.
As is understood by those skilled in the art, pinion gears 52 mounted on a pinion shaft 54
meshingly engage with both of the side gears 48, 50 and permit the wheels 20, 22 to turn
at different speeds during turning of the vehicle 10. A pinion gear 55 rotates with the
propeller shaft 30 and meshingly engages with a carrier 57 of the rear differential 24.
[0020] The power take-off module 16 includes two torque-transmitting
mechanisms in the form of friction clutches 56, 58, that, along with the hydraulic pump
38 and an electronic controller 110 (shown in Figures 3-5) form a transmission
distribution system 17 that transfers torque between left and right front wheels 20, 22 and
between front wheels 20, 22 and rear wheels 26, 28, as described hereinafter.
[0021] The friction clutch 56 is also referred to as an electronically-limited slip
differential clutch. A hub 59 extends from a right wheel shaft 60 that rotates with the
right side gear 50 and operatively connects to the right wheel 22. Hydraulic pressure
supplied from the pump 38 to an apply cavity 62 moves a piston 64 which provides an
axial force through a thrust bearing 66 to cause engagement of clutch plates splined to the
hub 59 with clutch plates splined to a second hub 68 that is connected for rotation with a
sleeve shaft 70 that rotates with the carrier 44. An additional thrust bearing 72 absorbs
axial force between the hub 68 and a portion of the module casing 18 (shown in
fragmented, cross-sectional view, but understood to be an integral casing as
schematically depicted in Figure 1). When the friction clutch 56 is released (i.e., not
engaged), the front differential mechanism 46 functions as an open differential.
[0022] The friction clutch 58, also referred to as an active-on-demand clutch, is
selectively engagable via hydraulic pressure provided by the hydraulic pump 38 to
connect a longitudinal shaft 74 for common rotation with propeller shaft 30. The
longitudinal shaft 74 is operatively connected to and driven by rotation of the sleeve shaft
70. Specifically, a set of intermeshing gears, including gear 76 mounted for rotation with
sleeve shaft 70 and gear 78 mounted for rotation with intermediate shaft 80 transfers
torque to a set of beveled gears including beveled gear 82 rotating with intermediate shaft

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80 and beveled gear 84 rotating with longitudinal shaft 74, permitting a 90 degree shift in
the axis of rotation between the sleeve shaft 70 and longitudinal shaft 74. Multiple
angular thrust bearings 86 absorb loads between the gears 78, 82, 84, shafts 74 and 80
and the casing 18. When the friction clutch 58 is released (i.e., not engaged) no torque is
sent to the rear differential mechanism 24.
[0023] A hub 88 extends from longitudinal shaft 74. Selective engagement of
friction clutch 58 is via hydraulic pressure from the pump 38 supplied to fill cavity 90 to
move piston 92 to engage friction plates extending from hub 88 with friction plates
extending from a hub 94 connected for rotation with propeller shaft 30. A roller bearing
96 is placed between propeller shaft 30 and casing 18. Thrust bearings 98 and 100,
transfer axial loading from the piston 92 to the friction plates and reaction loading from
hub 88 to housing 18, respectively.
[0024] Referring to Figure 3, hydraulic and electronic control of the
electronically-limited slip differential clutch 56 and the active-on-demand friction clutch
58 of Figure 2 is illustrated with respect to the respective clutch pistons 64 and 92. A
hydraulic control module 101 includes a valve body 102 within the casing 18 of the
power take-off unit 16. The valve body 102 houses electronically-controlled solenoid
valves 104 and 106. The pump 38 pressurizes fluid drawn from a fluid source 107, such
as a sump in the transmission casing 14, and is hydraulically connected with the solenoid
valves 104 and 106 via a fluid passage extending through a passage opening 108 (also
shown in Figures 1, 2, 4 and 5) formed by aligned apertures in the adjacent transmission
casing 14 and module casing 18. (In Figures 3-5, the transmission casing 14 and the
module casing 18 are depicted in phantom, and are only schematic, but represent the
same casings 14, 18 depicted in Figures 1 and 2.) Other alternative means to
hydraulically connect the pump 38 with the valve body 102 may be employed, such as an
external tube. The controller 110 receives input information signals 111 from the vehicle
10, also referred to herein as sensor signals, which may include information from a yaw
sensor, a steering wheel angle sensor, a lateral acceleration (G-force) sensor and wheel
speed sensors. The controller 110 is shown external to casings 14 and 18, but may be an
existing transmission controller housed in the transmission casing 14, a body module

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controller housed in a body of the vehicle 10, or a separate controller housed in the
module casing 18. The input information signals 111 are processed by the controller 110
according to an algorithm stored therein to determine whether either or both of the
friction clutches 56, 58 should be engaged to transfer torque, and the level of torque to be
transferred and corresponding amount of hydraulic pressure that should be provided. The
controller 110 provides control signals 112, 114 to move either or both of the respective
solenoid valves 104, 106 an amount correlated to the amount of hydraulic pressure
determined to be applied (movement is in a downward direction in Figure 3), thereby
allowing pressurized hydraulic fluid to reach fill cavity 62 and/or fill cavity 90 to engage
the respective clutches 56, 58. Accordingly, the hydraulic control module 101 is
electronically controlled by the controller 110 to vary the clutch capacity of the clutches
56,58.
[0025] Referring to Figure 4, an alternative embodiment of a hydraulic control
module 201 utilizes the same components as the hydraulic control module 101 of Figure
3, and adds a ball check valve 203, an accumulator 204 and an additional solenoid valve
206. Solenoid valves 104, 106 and 206 are included in valve body 202. The ball check
valve 203, accumulator 204 and additional solenoid valve 206 allow pressure to be stored
in the hydraulic lines or passages shown connecting the pump 38 with the fluid apply
chambers 62 and 90 of friction clutches 56, 58 of Figure 2, thus reducing clutch apply
time. The accumulator 204 stores pressurized fluid, as is known in the art. The ball
check valve 203 is biased (e.g., spring loaded) to prevent backflow of the pressurized
fluid to the sump 107 but is opened by a predetermined amount of fluid pressure
delivered from the pump 38 sufficient to overcome the bias. The first additional solenoid
206 is in a closed position when unactuated, with a ball check valve therein preventing
flow from the accumulator 204 to the solenoid valves 104, 106, thus maintaining stored
pressure in the accumulator 204 and the hydraulic lines or passages. The first additional
solenoid 206 receives a control signal 208 from the controller 110 actuating the solenoid
206 and causing it to open (by shifting to the left in Figure 4) to permit flow
therethrough.

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[0026] Referring to Figure 5, another alternative embodiment of a hydraulic
control module 301 utilizes the same components as the hydraulic control module 201 of
Figure 4, except that the ball check valve 203 is replaced with a solenoid valve 306 that
establishes, along with solenoid valves 104, 106 and 206, valve body 302. The solenoid
valve 306 responds to a control signal 316 from the controller 110 to permit pumped,
pressurized hydraulic fluid into the accumulator 204. The solenoid valve 306 allows
more active control of when line pressure is stored than does the ball check valve 203 of
Figure 4. Also, two pressure sensors 308 and 310 are added to monitor the clutch
pressure at the apply chambers 62, 90 of friction clutches 56, 58 of Figure 2, respectively.
The pressure sensors 308, 310 allow feedback clutch pressure control. Such pressure
sensors may be employed in each of the hydraulic control module embodiments
discussed herein.
[0027] Thus, referring again to Figure 1, the friction clutches 56, 58 are
controlled using hydraulic pressure from an engine-driven transmission pump 38 that is
also used to provide pressure to transmission friction clutches (not shown, but housed
within transmission casing 14, as is known in the art), and therefore allows torque
distribution regardless of a difference in wheel speed. The electronically-controlled
power take-off module 16 is relatively compact in size due to the absence of any
additional pump or pump motor. The torque distribution system 16 permits torque
distribution even when the vehicle wheels 20, 22, 26 and 28 are stationary, i.e., to assist
with torque distribution at launch.
[0028] While the best modes for carrying out the invention have been described
in detail, those familiar with the art to which this invention relates will recognize various
alternative designs and embodiments for practicing the invention within the scope of the
appended claims.

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CLAIMS
1. A torque distribution system for a vehicle having an engine,
wheels, and a hydraulic pump, comprising:
at least one torque-transmitting mechanism selectively engagable to
transfer torque between at least two of the wheels; wherein the hydraulic pump is
hydraulically connectable with said at least one torque-transmitting mechanism for
controlling engagement thereof; and
wherein the hydraulic pump is driven by the engine, thereby being
operable to provide hydraulic pressure for engagement of said torque-transmitting
mechanism even when the wheels are not rotating.
2. The torque distribution system of claim 1, wherein the vehicle
includes a transmission; and wherein the hydraulic pump provides hydraulic pressure to
the transmission.
3. The torque distribution system of claim 1, wherein the wheels
include a left front wheel and a right front wheel, and further comprising:
a first differential mechanism having a first member operatively connected
for driving rotation by an output member of said transmission, a second member
operatively connected for driving rotation of said left front wheel, and a third member
operatively connected for driving rotation of said right front wheel; and
wherein said at least one torque-transmitting mechanism includes a first
friction clutch selectively engagable to transfer torque between said second member and
said third member to thereby transfer torque between said left and right front wheels.
4. The torque distribution system of claim 1, wherein the vehicle
includes a transmission; wherein the wheels include left and right front wheels and rear

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wheels; wherein the hydraulic pump provides lubrication and hydraulic pressure to gear
selection clutches within the transmission; and further comprising:
a front differential mechanism operatively connected with said left and
right front wheels, respectively;
a longitudinally- extending member spanning at least partially between the
front and rear wheels;
a rear differential mechanism operatively connected with the rear wheels
and with the longitudinally-extending member; and
wherein the at least one torque-transmitting mechanism includes a first
clutch selectively engagable for transferring torque between said front differential and
said longitudinally-extending member to thereby transfer torque between the front and
rear wheels.
5. The torque distribution system of claim 1, wherein the vehicle
includes a transmission; wherein the wheels include left and right front wheels; wherein
said front differential mechanism has a carrier member driven by the transmission, left
and right side gears driven by said carrier member and operatively connected for rotation
with the left and right front wheels, and pinion gears meshing with both of the side gears;
and
wherein said at least one torque-transmitting mechanism includes a
friction clutch selectively engagable for transferring torque between said left and right
side gears of said front differential mechanism, thereby transferring torque between the
left and right front wheels.
6. The torque distribution system of claim 1, further comprising:
an electronic controller operative for receiving a sensor signal correlated
with at least one vehicle condition and for sending a control signal based on said sensor
signal and determinative of the hydraulic pressure applied to said at least one torque-

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transmitting mechanism, thereby permitting controlled slip of said at least one torque-
transmitting mechanism to vary an amount of torque transferred by said at least one
torque-transmitting mechanism.
7. The torque distribution system of claim 6, further comprising:
a hydraulic control module operatively connecting said controller with
said at least one torque-transmitting mechanism; wherein said hydraulic control module
includes at least one solenoid selectively actuatable by a control signal from said
controller to allow hydraulic pressure provided by said pump into fluid communication
with said at least one torque-transmitting mechanism.
8. The torque distribution system of claim 7, wherein said at least one
solenoid is a first solenoid, and further comprising:
an accumulator;
a check valve biased to prevent fluid communication of the hydraulic
pump with the accumulator and openable upon a predetermined hydraulic pressure from
the hydraulic pump to allow fluid communication of the hydraulic pump with the first
solenoid; and
an additional solenoid in fluid communication between the accumulator
and the first solenoid and selectively actuatable and configured to permit hydraulic flow
to said first solenoid when actuated and to prevent hydraulic flow to said first solenoid
and maintain hydraulic pressure in the accumulator when not actuated.
9. The torque distribution system of claim 7, wherein said at least one
solenoid is a first solenoid, and further comprising:
an accumulator;

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a first additional solenoid in fluid communication between the
accumulator and the first solenoid and selectively actuatable and configured to permit
hydraulic flow to said first solenoid when actuated and to prevent hydraulic flow to said
first solenoid and maintain hydraulic pressure in the accumulator when not actuated; and
a second additional solenoid in fluid communication between the
hydraulic pump and the accumulator and selectively actuatable and configured to permit
fluid communication of the hydraulic pump with the accumulator when actuated and to
prevent fluid communication of the hydraulic pump with the actuator when not actuated.
10. The torque-distribution system of claim 7, further comprising:
at least one pressure sensor operatively connected with said at least one
torque-transmitting mechanism and operable to monitor apply pressure of said at least
one torque-transmitting mechanism and communicate said monitored pressure to said
controller.
11. The torque distribution system of claim 1, wherein engagement of
said at least one torque-transmitting mechanism does not require braking of the vehicle.
12. The torque distribution system of claim 1, wherein said at least one
torque-transmitting mechanism includes friction plates and a piston movable by said
hydraulic pressure to engage said friction plates, and further comprising:
thrust bearings axially adjacent said friction plates for transmitting axial
force due to movement of said piston to engage said friction plates.
13. A torque distribution system for a vehicle having four wheels,
including a left front wheel and a right front wheel, and an automatic transmission with a
hydraulic pump, wherein the hydraulic pump provides hydraulic pressure to the
transmission, comprising:

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at least one torque-transmitting mechanism selectively engagable to
transfer torque between at least two of the wheels; wherein the hydraulic pump is
hydraulically connectable with said at least one torque-transmitting mechanism for
controlling engagement thereof;
wherein the hydraulic pump is driven by the engine, thereby being
operable to provide hydraulic pressure for engagement of said at least one torque-
transmitting mechanism even when the wheels are not rotating;
an electronic controller operative for receiving a sensor signal correlated
with at least one vehicle condition and for sending a control signal based on said sensor
signal and determinative of the hydraulic pressure applied to said at least one torque-
transmitting mechanism, thereby permitting controlled slip of said at least one torque-
transmitting mechanism to vary an amount of torque transferred by said at least one
torque-transmitting mechanism;
a hydraulic control module operatively connecting said controller with
said at least one torque-transmitting mechanism; and wherein said hydraulic control
module includes at least one solenoid selectively actuatable by a control signal from said
controller to allow hydraulic pressure provided by said pump into fluid communication
with said at least one torque-transmitting mechanism.
14. An electronically controlled power take-off module for a vehicle
having a transmission, an engine, a hydraulic pump, and a front and a rear differential
connected with front and rear wheels, respectively, comprising:
an active-on-demand clutch; wherein the hydraulic pump is driven by the
engine; wherein the active-on-demand clutch is selectively engagable via hydraulic
pressure provided by said hydraulic pump to transfer torque from the front differential to
the rear differential;

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an electronically-limited slip differential clutch selectively engagable via
hydraulic pressure provided by said hydraulic pump to transfer torque between the front
wheels; and
an electronic controller operatively connected to said clutches for varying
the amount of hydraulic pressure provided to permit modulation of the level of torque
transferred via engagement of one or both of said clutches.
15. The electronic power take-off module of claim 14, wherein the
hydraulic pump is within a transmission casing, and further comprising:
a module casing enclosing said clutches and connectable to the
transmission casing to permit fluid transfer from said transmission pump to said clutches
through said connected transmission casing and module casing.
16. The electronic power take-off module of claim 14, wherein said
electronic controller is operative for receiving a sensor signal correlated with at least one
vehicle condition and for sending a control signal based on said sensor signal and
determinative of the hydraulic pressure applied to one of said clutches; and further
comprising:
a hydraulic control module operatively connecting said electronic
controller with said one of said clutches; and wherein said hydraulic control module
includes at least one solenoid selectively actuatable by said control signal from said
controller to allow hydraulic pressure provided by said pump into fluid communication
with said one of said clutches.

A torque distribution system for a vehicle permits the transfer of torque
between vehicle wheels using a selectively engagable clutch that is hydraulically engaged
using hydraulic pressure provided by a hydraulic transmission pump driven by the
engine, allowing for enhanced system functionality and reduced part content in
comparison with known torque distribution systems. The system may include an "active-
on-demand" clutch that is selectively engagable to transfer torque between a front
differential and a rear differential (thereby transferring torque from the front wheels to
the rear wheels) as well as an electronically-limited slip differential clutch selectively
engagable to transfer torque from one front wheel to the other front wheel through the
front differential. Utilization of the transmission hydraulic pump allows pressure to be
provided to engage the clutch even when the wheels are stationary, i.e., to launch the
vehicle.